Method of making tubing structures



April 21, 1953 D. w. FENTRESS 2,635,330

METHOD OF MAKING TUBING STRUCTURES Filed Nov. 17, 1947 4 SheetsSheet lINVENT R. 1 J5 Zwz lflezdzld 9.e, qjM- April 21, 1953 D. w. FENTRESS2,635,330

METHOD OF MAKING TUBING STRUCTURES Filed Nov. 17, 1947 4 Sheets-Sheet 2I v 1 I 4/ INVENTOR -15 Ewdwrzdz ifiw April 21, 1953 D. w. FENTRESS2,635,330

METHOD OF MAKING TUBING STRUCTURES Filed Nov. 17, 1947 4 Sheets-Sheet 5IN VEN TOR.

java! @zzzdeZLEfflM April 21, 1953 D. w FENTRESS 2,635,330 METHOD OFMAKING TUBING STRUCTURES Filed Nov. 17, 1947 4 Sheets-Sheet 4 INVENTOR.Zkz/zd flewliezzfzwss BY Patented Apr. 21, 1953 METHOD OF MAKING TUBINGSTRUCTURES David Wendell Fentress, Barrington, Ill., assignor to ChicagoMetal Hose Corporation, Maywood, 111., a corporation of IllinoisApplication November 17, 1947, Serial-No. 786,407

4 Claims.

This invention relates to tubing structures, and to means and methodsfor effecting the fabrication thereof, and concerns particularly tubingof the flexible or corrugated type.

It isan object of the invention to provide a flexible or corrugatedtubing structure of improved construction and improved operatingcharacteristics, and to provide improved and readily operable means andmethods for eiiecting the tubing fabrication.

More specifically stated, it is an object of the invention to provide animproved corrugated tubing of spiral laminated construction, having ahigh degree of flexibility in relation to its strength and resistance tofluid bursting pressures.

Further objects of the invention are to provide animproved corrugatedtubing structure of the foregoing type, which will have requisite fluidtightness; and which is so reinforced that it will be durable inservice, and may be corrugated or convoluted without undue distortion ofthe wall surfaces, while still retaining a high degree of flexibility.

Various other objects, advantages and features of the invention will beapparent from the following specification when taken in connection withthe accompanying drawings, wherein certain preferred embodiments of theinvention are set forth for purposes of illustration.

In the drawings, wherein like reference numerals refer to like partsthroughout:

Fig. 1 is a perspective view, somewhat diagrammatic in form,illustrating means and methods for effecting the initial fabricatingstep in the construction of tubing in accordance with the presentinvention, and in accordance with one preferred embodiment thereof;

Fig. 2 is an enlarged transverse sectional view through the weldingsupport arbor and associated parts, as illustrated in Fig. 1, and takenas indicated by the line 2--2 thereof;

Fig. 3 is a view similar to Fig. l, but illustrating a further step inthe fabrication of the tubing;

Fig. 4 is an enlarged transverse sectional view through the arbor andassociated parts, taken as indicated by the line 4-4 of Fig. 3;

Fig. 5 is a view, similar to Figs. 1 andB, but illustrating a stillfurther step in the fabrication of the tubin Fig. 6 is an enlargedpartial section through the structure of Fig. 5, taken as indicated bythe line 65 thereof;

Fig. 7 is a longitudinal sectional view through the welding arbor,showing the tubing in the condition of Fig. 5, and taken as indicated bythe line 'l-| thereof;

Figs. 8 and 9 are views illustrating successive steps in effecting thecorrugation of the tubing, in accordance with the embodiment selectedfor illustration; V

Fig. 10 is an enlarged longitudinal sectional view through the tubingwall, illustrating the manner of welding and securing the several wallthicknesses Fig. 11 is a transverse sectional view through the tubingwall on a further enlarged scale, and taken as indicated by the line lHof Fig. 10; Fig. 12 is a view similar to Figs. 1, 3' and 5; butillustrating a modified embodiment;

Fig. 13 is a view, also similar to Figs. 1, 3 and 5, but illustrating astill further modified embodiment or structure;

Fig. 14 is an enlarged transverse sectional view through the weldingarbor and associated parts showing the structure of Fig. 13, and takenas indicated by the line M l 4 thereof;

Figs. 15-29 are views illustrating further modified embodiments of theinvention, incorporating means and methods for effecting localizedwelding of the outermost lamination to secure fluid-tightness withretained flexibility; Fig. 15 being a view similarto Fig. 5 showing thewelding of the outermost lamination by electric arc welding;

Fig. 16 is an enlarged sectional view of the structure of Fig. 15 on theline l'6l'6 thereof;

Fig. 17 is a view, similar to Fig. 5, illustratin the applicationof dualelectrode rollers for effecting the welding of the outermostlaminations. by electro-resistance welding;

Fig. 18' is an enlarged partial sectional view of the structure of Fig.1'7, on the line |'8l8 thereof;

Fig. 19 is a view also similar to Fig. 5 illustrating the welding of theoutermost laminations in accordance with the general principles ofprojection welding;

Fig. .20 is an enlarged sectional detail view of the structure of Fig.19 on the line 20-40 thereof Fig. 21 is an enlarged detail sectionalview of the'mandrel structure of Fig. 15;

Fig. 22 is a view, also similar to Fig. 5, illustrating the'welding ofthe outermost laminations by the use of an inserted electrode bar;

Fig. 23 is an enlarged sectional detail view of the structure of Fig. 22on theline 23-'23 thereof;

Fig. 24 is a View similar to Fig. 23 illustrating the welding of theoutermost laminations by dual electrode rollers in conjection with aninserted bar shunt conductor:

Figs. 25 and 26 are views similar to Figs. 23 and 24, respectively, butincorporating also the use of a projection welding wire; and

Figs. 27, 28 and 29 are longitudinal and transverse detail sectionalviews of the mandrel structure of Fig. 22; Figs. 28 and 29 being takenas indicated by the lines 28-28 and 29-49, respectively, of Fig. 27.

This application is a continuation-in-part of my copending application,Serial No. 711,351, filed November 21, 1946 and entitled TubingStructure and Method of Manufacture.

In certain instances tubing structures are required having a high degreeof flexibility in respect to their strength and resistance toburstingpressures. In such instances the use of tubing having a laminated wallstructure is indicated; the laminated wall having a strength or.resistance to bursting pressures which is roughly proportional to theover-all thickness of the composite wall, whereas the rigidity orresistance to flexibility of the tubing is likewise only a first powermultiple of the rigidity of each lamination. If the tubing isconstructed of a single wall of increased thickness, the rigidityvaries, roughly as the cube of the wall thickness so that in the case oftubing having a relatively thick wall a structure deficient in thenecessary flexibility may result.

While the use of laminated tubing is thus desirable in many instances,difficulty has been encountered in the production of satisfactoryflexible laminated tubing, particularly in connection with thefabrication and corrugation thereof. In accordance with the presentinvention satisfactory and readily operable means and methods areprovided for fabricating the laminated tube wall, and for effecting thereinforcement and securing thereof without unduly impairing flexibility,and in such manner that the tubing may be satisfactorily corrugated withsuch ty e of convolution as may be desired, without distortion orrupture of the tube wall surfaces.

Referring more specifically to the drawings, and first to the embodimentillustrated in Figs. 1-11, in Fig. *1 there is illustrated a su port andwelding mandrel Hi, the detailed construct on of which is best shown inFigs. 2 and '7. As shown, the mandrel or arbor is composed of threeexpansible-sections |-2, IA and is mounted upon a central shaft l8 whichmay be supported and rotatably driven in any desired manner by means notshown. A pair of end plates 2!) and 22 is provided at the'ends of themandrel, these end plates being provided with radial slots 24 adapted toreceive screws 26 carried by the several manfaces 34 suitably formed inthe opposite ends of the bores of the mandrel sections.

It will be seen that upon relative rotation of shaft [8 in respect tothe mandrel, the several sections thereof will be radially expanded to apredetermined size determined by the length of the slots 24, orpermitted to collapse to a smaller size to facilitate the removal of acompleted cylinder work piece from the mandrel. Normally and during theoperations presently to be described, the shaft 18 and the severalmandrel sections move as a unit, if and as the mandrel is rotated.

Referring further to Figs. 1 and 2, in fabricating the tubing a sheet 36is first drawn from a suitable supply source onto and around theexpanded mandrel ID by the rotation thereof. The sheet 36 is formed ofsuitable material, such as metal, of whichthe tubing is to befabricated, and has a length transversely of the mandrel axis determinedby the diameter of the tubing 7 to be formed and the number oflaminations desired, and a length axially of the mandrel determined bythe length of the tubing desired. The length of the mandrel I0 islikewise determined by the length of ,the tubing to be formed, and theexpanded diameter thereof determines the normal or mean diameter of thetubing prior to the corrugating operations. Tubing structures of variouslengths may be fabricated'in accordance with the invention to provideeither relatively long conduits or relatively short bellows, as may bedesired; and it is to be understood that the term tubing as herein useddenotes any desired length including relatively short structuressometimes referred to as bellows.

After slightly in excess of one complete convolution of the metal sheethas been drawn onto the mandrel, as shown in Fig. 2, a welding roller 38is engaged against the overlapped seam, the welding roller having beenpreviously Withdrawn from the mandrel during the initial windingoperation of the metal sheet, as will be understood. As the weldingroller is shifted longitudinally of themandrel, as indicated by thearrow in Fig. l, and welding current applied, a longitudinal seam Weldwill be provided extending lengthwise of the tubing, as indicated by thereference number lii. Suitable means may be pr'o'vided'for mounting thewelding roller, and for shifting the roller longitudinally of themandrel, or for shifting the mandrel longitudinally in respect to theroller, and for applying the welding current to the roller and to themandrel, in accordance with standard welding practice.

After the longitudinal weld Gil has been formed, the welding roller 38is vvithdrawn and rota-- tion of the mandrel structure resumed so as tofurther wind the sheet 35 upon the mandrel into several superimposedspiral laminations, as many as desired. The length of the sheet 36 issuch that the end =32 thereof will slightly overlap the welded seam idin the finished tubing (see Fig. 11) During the final revolution of themandrel, a pair of Welding rollers til and is engaged against the sheetat the opposite ends of the mandrel and welding current applied so as toform circular seam-resistance welds 33 and between the sheets at theopposite ends of the tubing. The rollers 4 and 45 may be continuouslyengaged against the sheet both during the initial Winding as shown inFig. 1, and during the subsequent winding, if desired, and if therollers are power driven they will aid in winding the sheet upon themandrel. For economy it is desirablethat the welding current onlybeapplied during the final revolution of the mandrel to form onecomplete circular seam-resistance Weld at each tubing end.

'lo further seal the tubing sheet and retain it in position during thesubsequent corrugating operations the trailing sheet edge 42 may next bespot welded into position as indicated at 52 in Figs. and 6. This spotweldingmay conveniently be efiected by means of a welding electrode 54engaged sequentially along the length of the mandrel at spacedintervals, and the welding current applied. The spot welds 52 arepreferably spaced apart a distance corresponding to the pitch of thetubing corrugations to be formed,

so that each spot weld will be at a predetermined position in theconvolution, as will subsequently appear. After the welding operationsthe tubing may be removed from the welding and support mandrel, byeffecting the collapse thereof as previously described.

The corrugations, either helical or. annular, may be formed in anydesired manner. As illustrated in Figs. 8 and 9 the corrugations in theparticular embodiment shown are annularly formed by a plurality ofsequential rolling operations between suitably formed shaping rollers.As shown, the tubing is first subjected at spaced intervals to theaction of a pair of complementary forming rollers 56 and 58 disposedinternally and externally of the tubing whereby to form sequentially, aplurality of annular corrugations or convolutions in the tubing. ToeiIect the further shaping of the convolutions into the desired form,they may be subjected to the action of further forming rollers 60 and62, as shownin Fig. 9, whereby to form the convolutions into the desiredfinal shape. As previously indicated, the means for forming theconvolutions may take various specific forms, for example as shown inDreyerPatent 1,879,663, dated September 27, 1932, or as shown inFentress Patent 2,306,018, dated December 22, 1942.

The details of the completed tubing'wall are illustrated in Figs. 10 and11. It will be seen that a corrugated tubing wall having a plurality ofspiral laminations is provided, the corrugations being annular and atriple ply wall structure being formed in the particular embodimentillustrated. The longitudinal seam weld 40 extends lengthwise of theentire tubing and forms a fluid seal extending lengthwise of the entiretube so that the spiral wall structure is positively sealed againstfluid leakage. However, it will be seen that this weld is formed onlybetween the two innermost wall thicknessesor laminations whereby theweld imparts only a minimum of rigidity to the structure. The remaininglaminations except for the innermost two are free to slide relative toeach other during the formation of convolutions, thus eliminating builtup stress and resistance to formation which would result in a similarthickness composed of one piece. Also, the laminations are free to sliderelative to each other during the flexing of the tube in service,permitting a high factor of flexibility and fatigue life.

The spot welds 52 extend through all laminations, but these areselectively positioned at the crests of the convolutions where flexingis a minimum during use of the tubing, so that these welds likewisereduce the flexibility of the tubing only a minimum amount.

The circular seam-resistance welds 4B and 5B likewise pass through alllaminations and provide a secure holding means for anchoring the tubingwalls together at the tubing ends. These welds are beyond the zone offlexing and hence do not interfere withthe shifting of the tube wallsduring the flexing movements.

The several welds, as heretofore discussed, provide a sufficient andfirm anchorage for the tubingwwalls so that no misalignment or un-.wanted distortion thereof takes place during corrugating operations,regardless of thespecific type of corrugating means which may beemployed. By this means a tubing structure isproduced of maximumstrength, maximum flexibility, and with accurately formed corrugationsor convolutions, to provide a resulting finished product of maximumeiiiciency which will maintain itself in alignment and fiex freely inuse.

In certain instances, wherein the very highest,

degree of flexibility is not required, it may be desirable to provideadditional anchorage for the tubing laminations prior to the corrugatingoperations. In such instances, as shown in Fig. 12, the spot welds 52may be replaced by a secand longitudinal seam-resistance weld asindicated at 52c. This weld may be formed by causing the welding roller28 to be projected longitudinally of the tubing a second time, after thefinal winding of the strip, so as to replace the spot welding 52 by alongitudinal seam weld 52a. In other words, as indicated in Fig.- 12, alongitudinal seam-resistance weld is first applied between the innermostlaminations of the tube, as in Fig. l, and a second longitudinalresistance weld 52a superimposed thereon after the final windingoperations.

In 13 and 14 a still further modified em-- bodiment is illustrated. Inthis instance after the longitudinal seam weld 40 has been formed, aspreviously described in reference to Fig. 1, and as the. finalconvolutions are being wound upon the mandrel, a plurality of weldingrollers 64 is engaged with the sheet along with the welding rollers and43 and welding current applied to form welds as indicated at 5%simultaneously with the formation of the circular seam-resistance welds48 and 50. The Welds 521) may be complete circular seam-resistancewelds, or spaced spot welds as indicated in Figs. 13 and 14, or only asingle spot weld, if desired, depending upon the time of application ofthe welding current. The welding rollers 54 are so positioned that thewelds 521) are lorrned at those portions of the tubing which will formthe tubing crests after thecorrugating operations. One welding roller 64may be provided for each tubing crest, or only for spaced tubing crests,as indicated in Fig. 13. By shifting the rollers 54 additional tubingcrests may be'welded as indicated by'the dotted welds 52b, aftertheformation of the welds 52b.

In Figs. 15-29 means and methods are illustrated for efiecting the seamwelding of the outer most tubing laminations, after the spiral wrappingoperations, by means of a weld which penetrates only the outermostlaminated walls. By this means a seam weld for the outer laminations isprovided, for insured fluid-tightness and maximum stability of thetubing, while at'the same time retaining the high flexibility providedby freely slidable laminated walls.

Referring first to Figs. l5. l6 and 21, the mandrel is in this instancecomposed of a plurality of radially shiftable sections i2, i4 and i6mounted upon a central shaft I8 as previously described; but the endplates 2% and 22a, corresponding to the mandrel end plates 20 and 22previously described, are in this instance provided with radiallyprojecting ears or lugs 73 defining slots for the reception of a pair oflongitudinally extending chill bars l2 and M engageable with the formedtubing on the opposite sides of the tubing end 42 to be welded.

A welding electrode 76 is provided, said elecacsasso trode having meansfor shifting it longitudinally of the tubing, or there being means forshifting the mandrel longitudinally beneath the electrode as desired.Upon the application of the welding current to the electrode and to themandrel, as diagrammatically indicated in Fig. 15, a longitudinal seamweld 53 will be formed extending longitudinally of the sheet end 42 toeffect the securing of the two outermost laminations. Due to thepresence of the chill bars, and by controlling the speed and currentdensity applied to the welding electrode, the weld 18 may be preventedfrom penetrating beyond the outermost laminations, whereby to retain.freedom of movement between the remaining tubing laminated walls 3% formaximum flexibility. f'he welding electrode 58 may either be of the arcwelding type, wherein the metal of the electrode is deposited in moltenform into the weld; or it may be the heliarc type wherein the electrodehas associated therewith means for projecting an inert gas around theweld during the application of the welding current, and wherein themetal of the electrode remains intact and an autcgenous weld is formedof the parent metal of the tube sheet. As illustrated in Fig. 16. theouter weld 57 may preferably be disposed at a point displacedsubstantially 90 from the inner seam weld 50, whereby to distribute therigidifying effects of the two welded seams substantially uniformly onthe tubing in reference to lateral and vertical bending. To facilitateremoval of the end plate 2%, for removal of the finished tubing, thescrews 25a are in this instance provided with T-shaped heads forselective alignment with the plate slots Eda.

In Figs. 1'7 and 18 an arrangement is disclosed for effecting theselective welding of only the outermost tubing laminations by means ofdual cooperative electrodes, preferably coupled with the use of meansfor localizing the welding operations to the desired work areas.

As shown in Figs. 17 and 18, a pair of roller electrodes 3S and 38a isin this instance preferably employed, the mandrel being insulated andthe roller electrodes being connected, respectively, to the oppositepoles of the welding transformer, as diagrammatically indicated in Fig.1'7. Also, as shown in Fig. 18, a layer 86 of insulating material isdisposed between the various laminations 36 of the tube sheet, the layer80 preferably forming a complete covering Or barrier wall between thetube sheet laminations except immediately adjacent the sheet end 52. Thelayer 8i! may comprise a separate sheet of insulating materialsuperposed in respect to the tube sheet and spirally wrapped therewith,or it may comprise an insulating coating painted or otherwise physicallyor chemically applied to the sheet except adjacent the immediate sheetend 42.

As'the welding rollers 38 and 38a are moved longitudinally of the sheetend, and the welding current applied, a weld as indicated at 82 will beformed longitudinally between the outermost sheet laminations, the closejuxtaposition of the electrodes and the insulating material 80cooperating to localize the weld between the outermost laminations,leaving the remaining tube laminations free for flexing in accordancewith the principles heretofore discussed. 'In Figs. 19 and 20 anarrangement is shown for accomplishing the selective welding of theoutermost laminations into a longitudinal seam weld utilizing principlesanalogous to those employed in projection welding. In this instance awire 8% is laid beneath the final lamination closely juxtaposed to thestrip end 52, the wire preferably being positioned by means of suitablelugs 86 formed on the mandrel end plates, similar to the lugs (0previously described.

As the welding roller 38 is moved longitudinally over the wire 36, andwelding pressure and current applied, the high resistance contactbetween the wire and the tube sheet will produce heating resulting inthe softening of the wire which under the pressure of the electrode willbecome formed into a longitudinal seam-resistance weld 88 between theoutermost tube laminations, the weld, however, being localized to theoutermost laminations directly contacted by the wire.

As in the case of the insulation all, previously described, the wire 8%is shown in the drawings in exaggerated size for illustrative purposes.As will be understood, the purpose of the wire is not to add metal butto localize the heating area be; tween the wall laminations. The wiremay in certain instances be very small, and after the completion of theweld 63 becomes substantially indistinguishable, and a part of the metalsheet material as in the case, for example, of the welds GO and 52previously described.

Referring to Figs. 22, 23 and 27-29, an arrangement is shown foreffecting the selective welding of the outermost tubing laminations bymeans of an inserted bar electrode extending longitudinally of thetubing beneath the outermost laminations.

As best shown in Figs. 27 and 28, the mandrel end plates 2% and 221) arein this instance provided with a slot or opening 9!] into which there isinserted an electrode bar 92 extending longitudinally of the tube. Thisbar is inserted into position just prior to the winding of the finaltube laminations, the mandrel section iBb being cut away as indicated at94, Fig. 29, to receive the deformation of the inner tube laminations.The bar electrode 52 may be on the order of ten times the stockthickness, the latter being for example only two or three thousandthsinches in the instance of thin walled tubing, and thicker in theinstance of heavier wall sections. Preferably the thickness of theelectrode bar is maintained as small as possible so as to minimize theinward deflections of the inner tube laminations to a negligible amount,such deflection being shown in an exaggerated degree in the drawings forillustrative purposes.

The mandrel is in this instance insulated and the poles of the weldingtransformer are connected, respectively, to the electrode bar and thewelding roller. As the roller is moved longi tudinally of the sheet endt2, a longitudinal seam-resistance weld will be formed as indicated at96 selectively between the outermost tube laminations. After theformation of the weld the electrode bar 92 may be removedlongitudinally, and if desired the circular end resistance welds A8 and59 then formed or completed.

In Fig. 24 an arrangement is illustrated employing a pair of juxtaposedelectrodes and an inserted shunt conductor or third conducting electrodefor efiecting the selective welding of the outermost tube laminations.

In this instance a pair of roller electrodes 38 and 38a is employed,similar to the arrangement of Fig. 17, the electrodes being selectivelyconnected to the opposite poles of the welding transformer. A shuntconductor bar 96 mounted in position similar to the electrode bar92pmviously described is employed to aid in transmitting the currentbetween the electrode rollers, whereby to localize and produce a singlelongitudinal seam-resistance weld Hi0- selectively between the outermosttubing laminations as the electrode rollers are moved longitudinally ofthe sheet end and the Welding current applied. After the formation ofthe weld the shunt conductor bar 98 may be removed, in a manner similarto the electrode bar 92 previously described.

Various of the means heretofore described for producing the selectivewelding of the outermost tubing laminations may be used in conjunction.Thus, in Fig. 25 an arrangement is illustrated combining the wire 84 ofFig. 20 with the electrode bar 92 of Fig. 23. In Fig. 26 an arrangementis shown combining the use of the wire 84 with the double electrodes 38and 39a and the shunt conductor 98 of Fig. 24, and including also theinsulating coating 89 as heretofore discussed in reference to Fig. 18.

It is obvious that various changes may be made in the specificembodiments set forth, and in the method steps stated, without departingfrom the spirit of the invention. The invention is accordingly not to belimited to the specific structures and methods shown and described, butonly as indicated in the following claims.

The invention is hereby claimed as follows:

1. The method of making a flexible tubing structure which compriseswrapping a tube sheet about a mandrel to size the tubing and provideportions thereof in overlapped relation, welding a longitudinal seamalong overlapped portions my means of a roller electrode while using themandrel as a cooperative electrode and also as a support for the wrappedsheet, wrapping the sheet in further convolutions about said mandrelwhich has a cut-away surface in the periphery thereof, engaging a rollerelectrode against the outer surface of the tube sheet adjacent themargin thereof to provide a second seam weld extending longitudinally ofthe tubing structure, forcing inner tube windings inwardly into thecut-away surface of the mandrel with the outermost laminations remainingin substantially tubular form and localizing the welding ourrent withinthe outermost laminations by means of an electrode bar within thecut-away surface of the mandrel and between the tube windings forcedinwardly thereof and the outermost laminations, and with the outersurface of the bar positioned to effect conformation of the innersurface of the outermost laminations with the outer surface of the innerlaminations when in tubing form.

2. The method of making a flexible tubing structure as claimed in claim1, including the step of convoluting the tubing along a predeterminedportion of its length to provide a convoluted and spirally laminatedtubing wall.

3. The method of making a flexible tubing structure as claimed in claim1, which includes the step of inserting a filament of welding mate rialbetween outermost laminations exteriorly of the inserted elongated barelectrode for localizing the welding current to the tubing in thevicinity of the filament to effect the second or outermost seam weld.

4. The method of making a flexible tubing structure as claimed in claim1, wherein the Welding current is localized and restricted within theoutermost laminations by interposing insulation selectively between thelaminations.

DAVID WNDELL FENTRESS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 979,460 Fulton Dec. 27, 1910 1,304,594 Patscheider May 27,1919 1,363,159 Murray et a1 Dec. 21, 1920 1,501,872 Tobey July 15, 19241,738,465 Wagner et al. Dec. 3, 1929 2,015,173 Andrus Sept. 24, 19352,331,504 Raymond et a1. Oct. 12, 1943 2,337,247 Kepler Dec. 21, 19432,358,291 Fentress Sept. 12, 1944 2,445,801 Partiot 1- July 27, 19482,539,237 Dreyer Jan. 23, 1951

